The invention relates to the field of generating custom-designed optical waveforms, and in particular to manipulating the pulse train from a mode-locked laser to generate a custom optical waveform.
Previous implementations of broadband frequency chirps for high-resolution laser radar (lidar) have involved sweeping tunable CW laser sources, resulting in relatively slow chirps (1.5 THz in hundreds of ms) that have nonlinear contributions that must be measured and compensated. There has been recent interest in using the frequency components of a mode-locked laser to generate arbitrary optical waveforms. All of the previous works in this field have utilized architectures requiring high-speed control of the amplitude and phase of each component using the Fourier transform relationship to generate the waveform of interest. The only way to shift the frequency of one component is to apply a linear phase ramp on one of the phase modulators, referred to as serrodyning. However, a phase modulator cannot be driven to an arbitrary phase, and so implementations of this strategy have required multiple waveform generators interleaved together to simulate a continuous linear phase ramp. These systems have only provided frequency offsets of 1 MHz.